<!DOCTYPE html>
<html lang="zh_CN">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script type="text/javascript">
    var a = 12;
    var b = a;

    b = 24;
    console.log(b);// 24

    console.log(a); // ? 12

</script>

</html>
